This is sort of like the question of whether "bug" refers only to a certain order of insects, or refers to all creepy crawly things.
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GEdgarMay 1 '12 at 14:56

Well, I'm certainly glad I read this question and its answers. I never had the faintest idea that turtles and tortoises weren't just different words for the same thing. I've always just used the terms completely interchangeably. I wouldn't be able to tell one from the other anyway…
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Janus Bahs JacquetMar 8 at 15:56

5 Answers
5

(I am writing as the spouse of a nationally recognized expert on wild turtles, tortoises and terrapins in the US.)

In the US there are 50 species of "chelonians" excluding sea turtles. Among experts they are identified by strict Latin taxonimic names when precise species identification is required. There is also a looser English taxonomy, but there is enough regional variation that experts fall back on Latin when confusion arises.

But, even experts in "casual" conversation use the word "turtle" to include "turtles, tortoises and terrapins"; e.g. "I study turtles."

Some non-experts refer to the shelled animals that live primarily in water (lakes, rivers and streams) as "turtles" and those that live primarily on land as "tortoises". However, in the US northeast, the most common land dweller is the "box turtle".

Bottom line, in casual conversations in the US the word "turtle" encompasses all those shelled creatures.

In discussion with passionate "turtle people" try to use the correct taxonomic name.

Yes. American speakers do use the term turtle to refer to both the land-based and marine reptiles. Whereas many (not all) BrEng speakers will differentiate between the two species.

I always thought it strange that the cartoon series my son used to watch, Teenage Mutant Ninja Turtles, back in the late 1980s was titled so. It was obvious that the four pizza-obsessed ninja turtles; Raphael, Leonardo, Donatello and Michelangelo performed their heroic deeds on land and and hardly ever in sea or freshwaters. Although I do remember they spent some time in the sewers....

And now nearly thirty years later, I find that Americans still prefer to use the term turtle. In The Big Bang Theory, season 8 episode 17, Amy and Sheldon make an important announcement:

Amy: We have some exciting news.Leonard: OKSheldon: As you know, Amy and I have been together a long time. And a lot of things that I never thought were possible; now seem possible.Penny: Okaaay...Amy: After a careful evaluation of our relationship, we decided that the time was right to take a step forward.Leonard: ... OKSheldon: Do you want to say it?Amy: Let's say it together.Sheldon and Amy: We're getting a turtle!

We then see the couple in a pet shop choosing a tortoise.

This is all the more remarkable considering that Sheldon and Amy are scientists, Sheldon a theoretical physicist while Amy a neurobiologist.

Neither are freshwater terrapins routinely distinguished from saltwater turtles or terrestrial tortoises. Given that most of North America is more than an hour’s drive from saltwater, this should be of no great surprise. It is probably a mistake to believe that people who do not distinguish “sea turtles” from “land turtles” from “lake turtles” are somehow falling into errors of naming.
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tchristMar 8 at 15:49

@tchrist I'm not suggesting that it is a mistake to classify all shelled reptiles (land-based and non) as such, but allow me to be still surprised that the term tortoise is still "unpopular" or "unknown" among American English speakers. No one suggests that porpoises and whales are not related, and yet we have different names for them. Perhaps that's not the best example I could come up with , but I think I've made my point.
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Mari-Lou AMar 8 at 15:59

a slow-moving reptile, enclosed in a scaly or leathery domed shell into which it can retract its head and thick legs.
• Family Testudinidae: numerous genera and species, including the European tortoise (Testudo graeca).

(also sea turtle) a large marine reptile with a bony or leathery shell and flippers, coming ashore annually on sandy beaches to lay eggs.
• Families Cheloniidae (seven species) and Dermochelyidae (the leatherback).

a freshwater reptile related to the turtles, typically having a flattened shell. Called terrapin in South Africa and India and tortoise in Australia.
• Order Chelonia: several families, in particular Emydidae and Kinosternidae.
• any reptile of this order, including the terrapins and tortoises.

It's then true that in American English the term turtle can be used to refer to an animal that in other English languages is called tortoise.
This is not something that happens only in American English, though. Also other languages have a word equivalent to turtle (In Italian tartaruga) and one equivalent to tortoise (in Italian testuggine), but the first can be used instead of the second (even if it is less accurate).
To notice also that, for example, in Italian the European tortoise is called tartaruga.

Let me add that in Japanese (my native language) there's no word specific for turtle or one for tortoise. The catch-all word is "kame"; if you need to specify whether it's a turtle or tortoise, a turtle is called "umi-game" meaning sea-kame and a tortoise is called "riku-game" meaning land-kame.
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YujiJan 27 '11 at 15:34

@kiamlaluno. Thank you for pointing out the Italian terms, which I keep mixing up anyway. I should think of the term used to indicate the ancient Roman military formation (testuggine) to be reminded of the correct word for the animal.
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PaolaApr 30 '12 at 23:36

Yes. American English often uses "turtle" for tortoise, in British English the two terms are not interchangeable, and (for what it's worth) Indian English often uses tortoise as the generic term for both turtles and tortoises. (The Hare and the Tortoise is never *The Hare and the Turtle, and Indian languages—and Japanese is similar according to a comment above—usually have the same words for both, and this is mapped to tortoise, not turtle.) So it varies from region to region.

As evidence, the Compact Oxford English Dictionary (UK) says, under tortoise that it's "Called turtle in North America", and the American Heritage Dictionary of the English Language gives, under tortoise, definition 1b saying "Chiefly British A terrestrial or freshwater chelonian."

“When we were little,” the Mock Turtle went on at last, more calmly, though still sobbing a little now and then, “we went to school in the sea. The master was an old Turtle—we used to call him Tortoise–—”

“Why did you call him Tortoise, if he wasn’t one?” Alice asked.

“We called him Tortoise because he taught us,” said the Mock Turtle angrily. “Really you are very dull!”

@Andrew: To be honest, wanting to quote Alice is the only reason I posted an answer. :p
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ShreevatsaRJan 27 '11 at 19:28

Also, in AmE, there're no hares, they're all called rabbits.
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MitchSep 6 '11 at 19:51

1

"...and this is mapped to tortoise". Perhaps for a BE audience. For a USA audience (as both your dictionaries tell you), it should properly be mapped to "turtle". Admittedly, the English spoken in India is more BE-looking, so it makes sense that they'd translate to BE terminology.
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T.E.D.Sep 21 '11 at 13:34

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@T.E.D.: I don't know what you mean by saying what "should" be done. I was describing what is done. And in any case English in India is written for an Indian audience, not British or American. (If I understand your argument correctly, for every American expression X, you could say "it should properly be Y [for a British audience]". Which may be true, but irrelevant.)
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ShreevatsaRSep 21 '11 at 14:20